1. Field of the Invention
The present invention relates to a fiber aggregate, which contains fine carbon fibers etc., and a fabricating method of the fiber aggregate.
2. Description of Related Art
Carbon nanotube (hereafter referred to as CNT) is a new carbon material discovered by Sumio lijima of NEC Corporation in 1991. CNT is a tube-like shaped carbon material having a diameter of several nanometers to several ten nanometers. CNT has a structure in which a graphite sheet having a network of six-membered rings of sp2-bonded carbon atoms is cylindrically wrapped. CNT has a pipe-like shape having a diameter of about 0.5 nm to 10 nm and a length of about 1 μm. It has been confirmed that single-walled nanotubes, each of which has one-atom-thick layer, and multi-walled nanotubes, each of which consists of multiple layers of graphite, exist as CNTs.
CNT has a chemically quite stable structure. It has been confirmed that CNTs exhibit various properties. For example, CNTs can be both of a good conductor and a semiconductor in accordance with a winding inclination of a spiral of hexagonal lattice that forms CNT. Moreover, CNT is excellent in electrical properties, in thermal conductivity and in mechanical strength. Applications of CNT to the fields of thermal equipment, electrical and electric equipment, etc. have been studied actively, taking advantage of these features.
However, due to the microstructure, handleability and processability of CNTs are bad. Thus, there have been attempts to fabricate a material that is formed of CNTs and has a size large enough to be handled under being checked by the naked eye. As examples in which CNTs are used as a raw material, textiles and sheets using CNTs are known. Moreover, there are proposed woven fabrics and sheets in which CNTs are partially or wholly used. In the woven fabrics and the sheets, CNTs are used as constituents of fibers or yarns (fiber aggregates) or as fibers or yarns themselves. Furthermore, there are disclosed technologies for fabricating yarns and sheets using vertically aligned CNTs.
Specifically, CNTs are formed on a substrate to be aligned in a direction perpendicular to the substrate. Then, by peeling and pulling a bundle of the CNTs away from the substrate, the yarns or the sheets are fabricated (see WO2005/102924A1 corresponding to US2008/0095694A1, for example).
It is considered to use the fiber aggregate, which consists of fine carbon fibers such as CNTs fabricated by the above-mentioned well-known technologies, as a conducting wire. The conducting wire features small diameter and light weight.
In order to use the fiber aggregate consisting of fine carbon fibers as a conducting wire, it is necessary to form a surface insulating layer on the fiber aggregate. In order to form the surface insulating layer, commonly an outside of the fiber aggregate is covered with insulating resin.
However, if the fiber aggregate consisting of fine carbon fibers is covered with resin, the diameter of the fiber aggregate is extended and the weight of the fiber aggregate is increased. Accordingly, the resin covering impairs the advantages of the fiber aggregate, i.e., the small diameter and the light weight when the fiber aggregate consisting of the fine carbon fibers is used as a conducting wire.